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Anacleto Formation
The Anacleto Formation is a geologic formation with outcroppings in the Argentine Patagonian provinces of Mendoza, Río Negro, and Neuquén. It is the youngest formation within the Neuquén Group and belongs to the Río Colorado Subgroup. Formerly that subgroup was treated as a formation, and the Anacleto Formation was known as the Anacleto Member.Sánchez et al. (2006) The type locality of this formation lies 40 kilometers west of the city of Neuquén. At its base, the Anacleto Formation conformably overlies the Bajo de la Carpa Formation, also of the Río Colorado Subgroup, and it is in turn unconformably overlain by the Allen Formation of the younger Malargüe Group.Fossa Mancini et al. (1938), Leanza et al. (2004) The Anacleto Formation varies between 60 and 90 meters thick, and consists mainly of claystones and mudstones, purple and dark red in color, of fluvial origin. Geodes are often found scattered throughout this formation.Leanza et al. (2004), Sánchez et al. (2006) Age Era: Mesozoic Period: Late Cretaceous Faunal stage: early Campanian Absolute Age: ~83 to ~78 mya Fauna '' with a human for size comparison]] ]] Nests of dinosaur eggs, many with preserved embryos inside, have been discovered in large quantities at the famous Auca Mahuevo locality, and have been attributed to titanosaurs.Salgado ''et al. (2005), Sánchez et al. (2006) Known from bones found in the Anacleto Formation are: * Aerosteon. * several species of lizards * an ornithopod (Gasparinisaura) * titanosaurian sauropods (Antarctosaurus wichmannianus, Pellegrinisaurus) * ceratosaurian theropods (Abelisaurus, Aucasaurus) * some other theropod remains * several species of mammals The oldest known unequivocal bird footprints from South America were also discovered in the Anacleto Formation. The small footprints were tentatively assigned to the ichnogenus Aquatilavipes and might have been produced by Patagopteryx (whose fossils were only found in the Bajo de la Carpa Formation however) or some unknown wader-like bird; they lack a hind toe. Ignotornis refers to similar footprints made by larger birds with a small hind toe; they might have been left by Neuquenornis, but this is also only known from the Bajo de la Carpa Formation. Footprints of these two ichnogenera have also been found elsewhere, but it must be understood that assignment to the same ichnogenus does not imply a close relatedness of the organisms that produced these traces, only a similar morphology.Coria et al. (2002), Lockley et al. (2006) Even smaller and somewhat unusual footprints assigned to Barrosopus are only known from the Anacleto Formation. They were almost certainly made by some tiny theropod, but whether this was a bird is not quite clear: the innermost front toes of the animal leaving these tracks attached in a position higher than the others. In that, and in their dimensions, they are a very close match for the odd-footed enantiornithine bird Yungavolucris brevipedalis, but this is only known from the Maastrichtian Lecho Formation which is some 10 million years younger.Chiappe (1993), Coria et al. (2002), Lockley et al. (2006) See also * List of fossil sites Footnotes References * Chiappe, Luis M. (1993): Enantiornithine (Aves) Tarsometatarsi from the Cretaceous Lecho Formation of Northwestern Argentina. American Museum Novitates 3083: 1-27. with Spanish abstract PDF fulltext * Coria, Rodolfo A.; Currie, Philip J.; Eberth, David & Garrido, Alberto (2002): Bird footprints from the Anacleto Formation (Late Cretaceous), Neuquén, Argentina. Ameghiniana 39(4): 453-463. with Spanish abstract PDF fulltext * Fossa Mancini, E.; Feruglio, E.; Yussen de Campana, J.C. (1938): Una reunión de geólogos de YPF y el problema de la terminología estratigráfica YPF geologists' reunion and the problem of stratigraphy terminology". Boletín de Informaciones Petroleras 15: 1-67. * Leanza, H.A.; Apesteguia, S.; Novas, F.E. & de la Fuente, M.S. (2004): Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages. Cretaceous Research 25(1): 61-87. (HTML abstract) * Lockley, Martin; Matsukawa, Masaki; Ohira, Hiroto; Li, Jianjun; Wright, Joanna; White, Diane & Chen, Peiji (2006): Bird tracks from Liaoning Province, China: New insights into avian evolution during the Jurassic-Cretaceous transition. Cretaceous Research 27(1): 33-43. (HTML abstract). Erratum: * Salgado, L.; Coria, R.A. & Chiappe, Luis M. (2005): Osteology of the sauropod embryos from the Upper Cretaceous of Patagonia. Acta Palaeontologica Polonica 50(1): 79–92. PDF fulltext * Sánchez, Maria Lidia; Heredia, Susana & Calvo, Jorge O. (2006): Paleoambientes sedimentarios del Cretácico Superior de la Formación Plottier (Grupo Neuquén), Departamento Confluencia, Neuquén paleoenvironments in the Upper Cretaceous Plottier Formation (Neuquen Group), Confluencia, Neuquén. Revista de la Asociación Geológica Argentina 61(1): 3-18. with English abstract PDF fulltext Category:Geology of Argentina Category:Geography of Mendoza Province Category:Geography of Neuquén Province Category:Cretaceous paleontological sites